# std::flat_multimap<Key,T,Compare,KeyContainer,MappedContainer>::emplace

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< cpp‎ | container‎ | flat multimap

template< class... Args > iterator emplace( Args&&... args ); |  | (since C++23)

Inserts a new element into the container constructed in-place with the given args.

Initializes an object t of type std::pair<key_type, mapped_type> with std::forward<Args>(args)...; if the map already contains an element whose key is equivalent to t.first, *this is unchanged. Otherwise, equivalent to:

    auto key_it = ranges::upper_bound(c.keys, t.first, compare);
    auto value_it = c.values.begin() + std::distance(c.keys.begin(), key_it);
    c.keys.insert(key_it, std::move(t.first));
    c.values.insert(value_it, std::move(t.second));

This overload participates in overload resolution only if std::is_constructible_v<std::pair<key_type, mapped_type>, Args...> is true.

Careful use of `emplace` allows the new element to be constructed while avoiding unnecessary copy or move operations.

| Information on iterator invalidation is copied from here

### Parameters

args | - | arguments to forward to the constructor of the element

### Return value

An iterator to the inserted element.

### Exceptions

If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).

### Complexity

Linear in the size of the container

### Example

Run this code

    #include <iostream>
    #include <string>
    #include <utility>
    #include <flat_map>

    int main()
    {
        std::flat_multimap<std::string, std::string> m;

        // uses pair's move constructor
        m.emplace(std::make_pair(std::string("a"), std::string("a")));

        // uses pair's converting move constructor
        m.emplace(std::make_pair("b", "abcd"));

        // uses pair's template constructor
        m.emplace("d", "ddd");

        // emplace with duplicate key
        m.emplace("d", "DDD");

        // uses pair's piecewise constructor
        m.emplace(std::piecewise_construct,
                  std::forward_as_tuple("c"),
                  std::forward_as_tuple(10, 'c'));

        for (const auto& p : m)
            std::cout << p.first << " => " << p.second << '\n';
    }

Output:

    a => a
    b => abcd
    c => cccccccccc
    d => ddd
    d => DDD

### See also

emplace_hint | constructs elements in-place using a hint (public member function)
try_emplace | inserts in-place if the key does not exist, does nothing if the key exists (public member function)
insert | inserts elements (public member function)

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